Software architecture is known to be an e , ective tool with regards to improving Software quality attributes. Many quality attributes such as maintainability are architecture dependent, and as such, using an appropriate architecture is essential in providing a sound foundation for the development of highly maintainable Software systems. An e , ective way to produce a well-built architecture is to utilize standard architectural patterns. Although the use of a particular architectural pattern cannot have a preserving e , ect on Software maintainability, the mere conformance of a system to any architecture cannot guarantee the system's high maintainability. The use of an inappropriate architecture can seriously undermine Software maintainability at lower levels. In this article, the e , ect of standard architectural patterns on Software maintainability quality attributes is investigated. We develop a quality model for maintainability quality attributes, which is later used to compare various standard architectural patterns. We , nish by investigating two real-world experiences regarding the application of a particular pattern to two di , erent existing architectures, exploring the e , ect of the change in architecture on maintainability quality attributes.